#define SENTINAL ((((uint64_t)1) << 63) - 1)

if (ops[0] == SENTINAL && ops[1] == SENTINAL) {
  back_array[0] = 0;
  back_array[1] = 0;
  return 3;  // should not generate any backpressure
} else if (ops[0] == ops[1]) {
  back_array[0] = 0;
  back_array[1] = 0;
  return 0;
} else if (ops[0] < ops[1] || ops[1] == SENTINAL) {
  back_array[0] = 0;
  back_array[1] = 1;
  return 1;
} else if (ops[1] < ops[0] || ops[0] == SENTINAL) {
  back_array[0] = 1;
  back_array[1] = 0;
  return 2;
} else {
  assert(0 && "not possible");
}

#undef SENTINAL
